This invention relates to a sensor with a laminated membrane that analyzes gasses dissolved in dielectric oil. In particular, this invention relates to a sensor that measures dissolved hydrogen with a laminated membrane that is resistant to pressure variations over the normal use of the sensor in, for example, electric transformers. This invention also relates to an apparatus that contains the sensor that measures dissolved gasses.
An apparatus for measuring hydrogen content and partial hydrogen pressure in gas streams is disclosed in U.S. Pat. No. 6,506,296 to Babes-Dornea. Other methods of measuring hydrogen dissolved in liquids are disclosed in U.S. Pat. No. 4,271,474 and U.S. Pat. No. 4,293,399 to Belanger. The use of micro fuel cell sensors to measure dissolved gasses in oil is well know in the art. Typically, a micro fuel cell comprises two electrodes separated by an electrolyte. These devices also contain polymer membranes that allow dissolved gasses to permeate through, but not the oil the gasses are dissolved in. The polymer membranes contained in these devices are very sensitive, as they vary in thickness from only about 25 to about 250 microns (1 and 10 mils).
Standard micro fuel cell sensors, as typically used in the industry, are attached to devices that contain dielectric oil, like an electric transformer. Over the normal course of operation, these sensors see wide changes in temperature and pressure. These variations in temperature and pressure can cause damage to these polymer membranes. In order to overcome the high-pressure effects, the circular shape polymeric membrane can be supported by a porous metallic disc. The sensors with supported membranes can withstand positive pressures up to about 10.3 MPa or 1500 psi without significant damage to the membrane.
The membranes supported inside the sensor are protected against the positive pressure applied, while remaining vulnerable to negative pressures (vacuum), created when the outside pressure becomes smaller than the pressure inside the sensor. The negative pressure situations create stresses on the membranes that cause them to rupture. Once the membrane is ruptured, the sensor becomes “flooded” with dielectric oil, which causes the sensor to fail. These vacuum occurrences, which account for ˜80% of sensor failures during field operations, usually arise during transformer maintenance. Further, temperature variations during operation cause thermal expansion and contraction of the thin membranes that affect their permeability and thus, sensor reliability. The membrane side facing the oil can't be protected with a porous disc (outside the detector) because the porous structure would be soaked with oil, further hindering the gas circulation towards the membrane.
Therefore, a need exists for a polymer membrane that allows the sensor to be serviced and utilized over normal operations and maintains reliability and prevents failure. Finally, a further need exists to develop an apparatus that contains the micro fuel cell sensor that will measure the dissolved gasses in dielectric oil.